Modelling the thermal conductivity of (U Th1−)O2 and (U Pu1−)O2

Abstract

a b s t r a c tThe degradation of thermal conductivity due to the non-uniform cation lattice of (U x Th 1Àx )O 2 and (U x Pu 1Àx )O 2 solid solutions has been investigated by molecular dynamics, using the non-equilibrium method, from 300 to 2000 K. Degradation of thermal conductivity is predicted in (U x Th 1Àx )O 2 and (U x Pu 1Àx )O 2 as compositions deviate from the pure end members: UO 2 , PuO 2 and ThO 2 . The reduction in thermal conductivity is most apparent at low temperatures where phonon-defect scattering dominates over phononephonon interactions. The effect is greater for (U x Th 1Àx )O 2 than for (U x Pu 1Àx )O 2 due to the greater mismatch in cation size and mass. Parameters for analytical expressions have been developed that describe the predicted thermal conductivities over the full temperature and compositional ranges. These expressions may be used in higher level fuel performance codes.Published by Elsevier B.V.

Effect of thorium addition on the thermophysical properties of uranium dioxide: Atomistic simulations

“…Hence, the MD simulation techniques provide a useful means to simulate such extreme conditions. As far as we know, the thermophysical properties of UO 2 [35][36][37][38][39], ThO 2 [30][31][32][33][34], and (U, Pu)O 2 [40][41][42][43] have been predicted by MD method over a wide temperature, and the evaluated results are almost in good agreement with the experimental values.…”

“…A poor thermal conductivity will leads to a large temperature gradient across the fuel pellet. However, to the best of our knowledge, the available literature data shows that the lattice parameter [10][11][12][13][14][15], thermal expansion [16][17][18][19], enthalpy increments data [20][21][22][23][24], specific heat capacity [22][23][24][25][26] and thermal conductivity [14,18,22,23,[27][28][29][30][31][32] of U 1-y Th y O 2 solid solution exist over a limited composition and temperature ranges.…”

Multiphysics modeling of UO2-SiC composite fuel performance with enhanced thermal and mechanical properties

“…A large number of materials have been proposed including carbon (in the form of graphite, diamond and nano-tubes) [5] [6], ceramics (such as ThO 2 , SiC, UN and BeO) [7]- [10], and some high temperature metals in various configurations such as homogenous or heterogeneous materials or heat-pipes [11].…”

“…However, the thermal conductivity of thorium-dioxide is only slightly higher than that of UO 2 , and therefore requires large volume fractions in order to observe a meaningful improvement. In fact, some homogenous mixtures of (U,Th)O 2 can actually have lower thermal conductivity compared to pure UO 2 , depending on the composition [7].…”

“…The model predicts significant reduction in fuel temperature, fission gas release and cladding strain, including a roughly 370 K reduction in fuel centerline temperature and a 66.7% reduction in fission gas release from UO 2 -13.6wt%BeO fuel case at fuel burnup of 600 MW*h/kg-U, thereby improving fuel margins. In 2013, a series of UO 2 -SiC composite fuel pellets with different sizes and volumetric fractions of SiC particles was fabricated by Yeo [7], and the thermal conductivities of the composite fuels were measured and compared to the results determined by theoretical formulations available in the literature.…”